Every day, the body is bombarded with bacteria, viruses and other infectious agents. When a person is infected with a disease-causing or infectious agent, the body's immune system attempts to mount a defense against it. When the defense is successful, immunity against the infectious agent results. When the defense is not successful, an infection may result.
In the process of developing immunity to the infectious agent, the B cells of the body produce substances known as antibodies that act against the specific infectious agent and create a “memory” of this experience that can be called upon for protection when exposed to the same infectious agent again months or years later. The next time the person encounters this particular infectious agent, the circulating antibodies quickly recognize it and enable it to be eliminated from the body by other immune cells before signs of disease develop. It is estimated that antibodies which can recognize over 10,000 different antigens or foreign (non-self) infectious agents are circulating in the blood stream.
A vaccine works in a similar way in that it produces an immunogenic response. However, instead of initially suffering the natural infection and risking illness in order to develop this protective immunity, vaccines create a similar protective immunity without exposing the body to the disease.
Development of vaccines against both bacterial and viral diseases has been one of the major accomplishments in medicine over the past century. While effective vaccines have been developed for a large number of diseases, the need for development of safe and effective vaccines for a number of additional diseases remains.
Several basic strategies are used to make vaccines. One strategy is directed toward preventing viral diseases by weakening or attenuating a virus so that the virus reproduces very poorly once inside the body. Measles, mumps, rubella (German measles) and chickenpox (varicella) vaccines are made this way. Whereas natural viruses usually cause disease by reproducing themselves many thousands of times, weakened vaccine viruses reproduce themselves approximately 20 times. Such a low rate of replication is generally not enough to cause disease. Although the preparation of live, attenuated infectious agents as vaccines will often provide improved immunologic reactivity, such methods do increase the risk that the vaccine itself will be the cause of infection, and that the attenuated organism will propagate and provide a reservoir for future infection. One or two doses of live “weakened” viruses may provide immunity that is life long; however, such vaccines cannot be given to people with weakened immune systems.
Another way to make viral vaccines is to inactivate the virus. By this method, viruses are completely inactivated or killed using a chemical. Killing the virus makes the virus unable to replicate in a body and cause disease. Polio, hepatitis A, influenza and rabies vaccines are made this way. The use of inactivated or killed bacterial or viral agents as a vaccine used to induce an immunogenic response, although generally safe, will not always be effective if the immunogenic characteristics of the agent are altered. An inactive virus can be given to people with weakened immune systems, but must be given multiple times to achieve immunity.
Vaccines may also be made using parts of the virus. With this strategy, a portion of the virus is removed and used as a vaccine. The body is able to recognize the whole virus based on initial exposure to a portion of the virus. The hepatitis B vaccine for example, is composed of a protein that resides on the surface of the hepatitis B virus.
Vaccines are also made to help combat diseases caused by bacteria. Several bacterial vaccines are made by taking the toxins produced by bacteria and inactivating them using chemicals. By inactivating the toxins, the bacteria no longer causes disease. Diphtheria, tetanus and pertussis vaccines are made this way. Another strategy to make bacterial vaccines is to use part of the sugar coating (or polysaccharide) of the bacteria to induce the immunogenic response. Protection against certain bacteria are based on responsive immunity to this sugar coating.
Thus, one must generally choose between improved effectiveness or greater degree of safety when selecting between the inactivation and attenuation techniques for vaccine preparation. The choice is particularly difficult when the infectious agent is resistant to inactivation and requires highly rigorous inactivation conditions which are likely to degrade the antigenic characteristics which help to induce an immune response and provide subsequent immunity.
In addition to the dead or weakened infectious agent, vaccines usually contain sterile water or saline. Some vaccines are prepared with a preservative or antibiotic to prevent bacterial growth. Vaccines may also be prepared with stabilizers to help the vaccine maintain its effectiveness during storage. Other components may include an adjuvant which helps stimulate the production of antibodies against the vaccine to make it more effective.
Methods to prepare vaccines today involve treating samples with glutaraldehyde or formaldehyde to fix or cross-link the cells or infectious particles. Such treatments generally involve denaturation of the native forms of the infectious particles. A disadvantage to this approach is that the protein coats of the infectious particles are damaged by this process, and thus may not be recognized by the immune system.
Therefore, the need exists for a method to prepare vaccines that are recognized by the immune system but do not replicate once inside the body.
The use of photosensitizers, compounds which absorb light of a defined wavelength and transfer the absorbed energy to an energy acceptor, are known to be useful in the sterilization of blood components. For example, European Patent application 196,515 published Oct. 8, 1986, suggests the use of non-endogenous photosensitizers such as porphyrins, psoralens, acridine, toluidines, flavine (acriflavine hydrochloride), phenothiazine derivatives, and dyes such as neutral red, and methylene blue, as blood additives. Protoporphyrin, which occurs naturally within the body, can be metabolized to form a photosensitizer; however, its usefulness is limited in that it degrades desired biological activities of proteins. Chlorpromazine, is also exemplified as one such photosensitizer; however its usefulness is limited by the fact that it should be removed from any fluid administered to a patient after the decontamination procedure because it has a sedative effect.
Goodrich, R. P., et al. (1997), “The Design and Development of Selective, Photoactivated Drugs for Sterilization of Blood Products,” Drugs of the Future 22:159–171 provides a review of some photosensitizers including psoralens, and some of the issues of importance in choosing photosensitizers for decontamination of blood products. The use of texaphyrins for DNA photocleavage is described in U.S. Pat. No. 5,607,924 issued Mar. 4, 1997 and U.S. Pat. No. 5,714,328 issued Feb. 3, 1998 to Magda et al. The use of sapphyrins for viral deactivation is described in U.S. Pat. No. 5,041,078 issued Aug. 20, 1991 to Matthews, et al. Inactivation of extracellular enveloped viruses in blood and blood components by Phenthiazin-5-ium dyes plus light is described in U.S. Pat. No. 5,545,516 issued Aug. 13, 1996 to Wagner. The use of porphyrins, hematoporphyrins, and merocyanine dyes as photosensitizing agents for eradicating infectious contaminants such as viruses and protozoa from body tissues such as body fluids is disclosed in U.S. Pat. No. 4,915,683 issued Apr. 10, 1990 and related U.S. Pat. No. 5,304,113 issued Apr. 19, 1994 to Sieber et al. The reactivity of psoralen derivatives with viruses has been studied. See, Hearst and Thiry (1977) Nuc. Acids Res. 4:1339–1347; and Talib and Banerjee (1982) Virology 118:430–438. U.S. Pat. Nos. 4,124,598 and 4,196,281 to Hearst et al. suggest the use of psoralen derivatives to inactivate RNA viruses, but include no discussion of the suitability of such inactivated viruses as vaccines. U.S. Pat. No. 4,169,204 to Hearst et al. suggests that psoralens may provide a means for inactivating viruses for the purpose of vaccine production but presents no experimental support for this proposition. European patent application 0 066 886 by Kronenberg teaches the use of psoralen inactivated cells, such as virus-infected mammalian cells, for use as immunological reagents and vaccines. Hanson (1983) in: Medical Virology II, de la Maza and Peterson, eds., Elsevier Biomedical, New York, pp. 45–79, reports studies which have suggested that oxidative photoreactions between psoralens and proteins may occur. Wiesehahn et al. discloses in U.S. Pat. Nos. 4,693,981 and 5,106,619 the use of psoralens to prepare inactivated viral vaccines. These patents disclose preparing vaccines by treating viruses with furocoumarins and long wavelength UV light for a time period sufficiently long enough to render the virus non-infectious but less than that which would result in degradation of its antigenic characteristics under conditions which limit the availability of oxygen and other oxidizing species. Swartz discloses in U.S. Pat. No. 4,402,318 a method of producing a vaccine by adding methylene blue and exposing the vaccine to light and an electric field concurrently to completely inactivate the viruses, bacteria, cells and toxins. Dorner et al. in U.S. Pat. No. 6,165,711 discloses a process for disintegrating nucleic acids to make vaccines by exposing biologically active material to phenothiazine and a laser beam.
The mechanism of action of psoralens is described as involving preferential binding to domains in lipid bilayers, e.g. on enveloped viruses and some virus-infected cells. Photoexcitation of membrane-bound agent molecules leads to the formation of reactive oxygen species such as singlet oxygen which causes lipid peroxidation. A problem with the use of psoralens is that they attack cell membranes of desirable components of fluids to be decontaminated, such as red blood cells, and the singlet oxygen produced during the reaction also attacks desired protein components of fluids being treated.
U.S. Pat. No. 4,727,027 issued Feb. 23, 1988 to Wiesehahn, G. P., et al. discloses the use of furocoumarins including psoralen and derivatives for decontamination of blood and blood products, but teaches that steps must be taken to reduce the availability of dissolved oxygen and other reactive species in order to inhibit denaturation of biologically active proteins. Photoinactivation of viral and bacterial blood contaminants using halogenated coumarins is described in U.S. Pat. No. 5,516,629 issued May 14, 1996 to Park, et al. U.S. Pat. No. 5,587,490 issued Dec. 24, 1996 to Goodrich Jr., R. P., et al. and U.S. Pat. No. 5,418,130 to Platz, et al. disclose the use of substituted psoralens for inactivation of viral and bacterial blood contaminants. The latter patent also teaches the necessity of controlling free radical damage to other blood components. U.S. Pat. No. 5,654,443 issued Aug. 5, 1997 to Wollowitz et al. teaches new psoralen compositions used for photodecontamination of blood. U.S. Pat. No. 5,709,991 issued Jan. 20, 1998 to Lin et al. teaches the use of psoralen for photodecontamination of platelet preparations and removal of psoralen afterward. U.S. Pat. No. 5,120,649 issued Jun. 9, 1992 and related U.S. Pat. No. 5,232,844 issued Aug. 3, 1993 to Horowitz, et al., also disclose the need for the use of “quenchers” in combination with photosensitizers which attack lipid membranes, and U.S. Pat. No. 5,360,734 issued Nov. 1, 1994 to Chapman et al. also addresses this problem of prevention of damage to other blood components.
Photosensitizers which attack nucleic acids are known to the art. U.S. Pat. No. 5,342,752 issued Aug. 30, 1994 to Platz et al. discloses the use of compounds based on acridine dyes to reduce parasitic contamination in blood matter comprising red blood cells, platelets, and blood plasma protein fractions. These materials, although of fairly low toxicity, do have some toxicity e.g. to red blood cells. This patent fails to disclose an apparatus for decontaminating blood on a flow-through basis. U.S. Pat. No. 5,798,238 to Goodrich, Jr., et al., discloses the use of quinolone and quinolone compounds for inactivation of viral and bacterial contaminants.
Binding of DNA with photoactive agents has been exploited in processes to reduce lymphocytic populations in blood as taught in U.S. Pat. No. 4,612,007 issued Sep. 16, 1986 and related U.S. Pat. No. 4,683,889 issued Aug. 4, 1987 to Edelson.
Riboflavin (7,8-dimethyl-10-ribityl isoalloxazine) has been reported to attack nucleic acids. U.S. Pat. Nos. 6,258,577 and 6,277,337 issued to Goodrich et al. disclose the use of riboflavin and light to inactivate microorganisms which may be contained in blood or blood products. U.S. Pat. No. 6,268,120 to Platz et al. discloses riboflavin derivatives which may be used to inactivate microorganisms.
All publications referred to herein are hereby incorporated by reference to the extent not inconsistent herewith.